stuffer tubes

[Justin]

Is there a rule of thumb?...Or an exact rule?
How big a BT can you run without a stuffer tube? Do I need one with an 18" BT 60? Any help would be great.

 

[eugenefl]

Originally posted by Justin
Is there a rule of thumb?...Or an exact rule?
How big a BT can you run without a stuffer tube? Do I need one with an 18" BT 60? Any help would be great.

Justin, I'm sure there is a formula out there that identifies the max possible volume of area for an ejection charge before it fails. In terms of what you are asking, no - you won't need a stuffer tube for an 18" BT60. If you have the extra tubing and a 3rd centering ring, go for it. Otherwise, you should be just fine installing the motor mount without the stuffer tube extension.

By the way, WELCOME TO THE ROCKETRY FORUM!

So whatcha buildin'?

 

[LarryH]

There are no motors made that fit directly into a BT-60, so yes you WILL need a motor mount tube, a few that come to mind that will work as motor mount tubes.... or can simply be used as airframes for minimum diameter rockets(no motor tube) are BT-5, this is a 13mm ID tube that works with 1/4-A, 1/2-A and some full A motors. BT-20 is an 18mm ID tube, it will fit A, B, and C motors. BT-50 is a 24mm ID tube, it will work with high thrust C motors(like the C-11), D, E, and some F motors. BT-55 is a 29mm ID tube that will hold F and G motors..... also H and some I motors, but you need THICK walls to contain the H and I motors.



Edit: wasn't really sure what you were asking, did you mean the entire motor tube or just the stuffer end? If you meant the later then I think I can safely say at this level it doesnt really matter, My Executioner which is a 2.6" diameter rocket has a huge 16" long void between the forward end of the MMT and the NC, my PE Patriot which is a 4" diameter rocket has about 11" between the forward end of the MMT and forward end of the airframe, now that's a pretty big void, and it actually uses a 1/8" hole drilled into the airframe to vent off the excess gas! I like a long stuffer tube personally because I can get a little wadding into it, but I dont think you'll run into problems with the recovery charge running out of gas before it ejects the NC.

 

[Justin]

Thanks for the welcome and help guys-
Euegenefl- I really like scale stuff, but I'm doing a work horse flyer thats kinda like a comercial space payloader. It's gonna run on d's and e's, and hopefully work. It's paint will not be scale like. It's time to use up the pile'o spray paint! Wish me luck..

Larryh-If I wrote you a couple years ago, you would have saved me a lot of time figuring out engine stuff! Thanks for replying.
I just didn't know if I could just stick in the motor mount and have enough energy to eject a chute from that tube. It's cool you took the time to lay it out for me. Thanks again..

 

[astronboy]

I like to add stuffer tubes to my longer rockets for a different reason.

I am presently building a scale model of the Redstone missile: 25" long, BT-70 for the bottom main airframe, transitioning to a BT-60 at the top. I have enslosed a picture of the 'innards' of this beasty. The motor mount and stuffer tube are heavywall BT-50 for 24mm D, E and F engines. The BT-60 section at top is the 'recovery device section' or as I like to call it, the laundry basket. The stuffer tube helps the chute from sliding down deep into the BT during acceleration (esp with the kick delivered by an F21!!)

 

[Fore Check]

Originally posted by Justin
Thanks for the welcome and help guys-
Euegenefl- I really like scale stuff, but I'm doing a work horse flyer thats kinda like a comercial space payloader. It's gonna run on d's and e's, and hopefully work. It's paint will not be scale like. It's time to use up the pile'o spray paint! Wish me luck..

Larryh-If I wrote you a couple years ago, you would have saved me a lot of time figuring out engine stuff! Thanks for replying.
I just didn't know if I could just stick in the motor mount and have enough energy to eject a chute from that tube. It's cool you took the time to lay it out for me. Thanks again..

You should be just fine with no stuffer in an 18" bt60, particularly if powered by a 24mm "D" or "E" engine.

For what it's worth, I can think of a couple of Estes products that use a stuffer tube in a BT60 based rocket. In both cases, the engine tube is about 8.5" long (instead of the minimum 2.75") Also, in both cases, it is for an 18mm (A-B-C) motor mount (the rockets are the Big Bertha and the Citation Patriot.)

Perhaps a better way of assuaging your concern would be to take a couple of other Estes tried-and-true examples of 24mm engine models that employ stuffer tubes, compute the interior volume of the airframe tube above the forward most ring of the stuffer tube, and apply that volume to your BT60 in determining if a stuffer is necessary in your model. This does assume, of course, that the design of the two Estes kits that I will use in this example are designed appropriately and that the key factor affecting recovery deployment is the interior volume of the airframe tube above the stuffer.

Let's take the Der-V3. It is BT80 based, with the body tube being about 14.25" long. It uses a 24mm motor mount built as an 7.75" long stuffer tube. Ignoring the shoulder of the nose cone, that leaves 6.5" of airframe tube above the stuffer. Without showing all the math, that leaves an interior volume of about 33.5 cubic inches. I can tell you from experience that the design of the Der-V3 works quite well. If you take that 33.5 cubic inches and back it into a BT60 rocket, that equates to about 16.75" in airframe tube length above the motor mount (again ignoring the shoulder length of the nose cone.) If you use an "E" engine in your rocket, which is 3.75" long, and do not build a stuffer, your tube above the engine will be 14.25" (which is less than the length backed in to of 16.75".) By this logic, you should be just fine.

The other example I was thinking of is the Estes Optima. It leaves 12.75" of airframe tube above the stuffer (ignoring the nose cone shoulder). This is nearly double the interior volume of the example of the Der-V3, so again you should be fine. I've never flown an Optima with a single engine (mine is a 3-engine cluster) - but reports on EMRR indicate that the recovery deployment works fine as designed (although the rocket is vastly underpowered in that design - which is another matter altogether.)


The other factor that a stuffer tube can help you with is the "holding" of your recovery system in the forward end of the rocket. This is independant of deployment issues - it is more for stability and the desire to keep your recovery system closer to the deployement end to further decrease any chances of mishaps. If these items are important to you, a stuffer will help - although it appears that your ejection charge will be sufficient to deploy your chute without the stuffer.

Hope this helps!

 

[powderburner]

Justin,
You already have a whole bunch of good advice posted here, so I am not going to repeat. I will say this much---take a look at the tall (six foot?) monsters offered by Estes and FlisKits---they do not use stuffers and they have no problem with popping out the parachutes.
But Astronboy and Fore Check raise a very important point; the front end of the stuffer tube can also function as a device to hold the weight of your recovery system forward.
If you don't want to mess with the cost/weight/complexity of installing a stuffer tube for purposes of holding the guts in the front end, you might want to consider building a baffle insert and locating it about six or eight inches inside the front end---that will also keep your recovery stuff in the nose, and save on wadding at the same time.

 

[LarryH]

I think a better rule of thumb is to calculate the weight of the recovery system and the nosecone to be deployed instead of worrying only about the volume that has to be filled, bottom line is the heavier the ejecta the closer you'll want the forward end of your motor tube to it, but even here I think you'll find that by the time your NC and recovery system is heavy enough to where you'll actually 'need' a stuffer tube that the rocket wont get off the pad anyway because of all the excess weight.

 

[Justin]

Great advice guys-
I'm gonna build a "laundry basket" like astronboy I think.

Fore Check- I just cannibalized a Big Bertha. Maybe I should have actually looked at it while I was scavenging.

Thanks everyone.

 

[prowlerguy]

The Stormcaster also uses a stuffer tube. It is a pretty long rocket, but only a BT-55.

 

[Chr$]

Are you using the stuffer to keep the laundry up top or to ensure enough pressure for ejection?

Just something to keep in mind is that an Estes Mean Machine is a 6 ft tall BT-60 and has no stuffer tube but gets the laundry out just fine.

The pic youposted of the innards looks just fine. I have a cluster Scratch build that has a BT20 transitioning to a BT-60 at the top, similar to your stuffer to BT-60 transition. It Keeps the CG just right and gives enough space for a large enough chute.

 

[Justin]

edit- I realized later this post was directed to astron boy, not me..Whoops..
Chr$-
At first I didn't know if I needed a stuffer at all, but after reading everyone's replies I decided to use one to keep weight up front, seeing as The Red Delta2 (official name now) has a lot going on in the rear of the ship. I'm fairly certain it would work fine without one though, thanks to the Rocketry Forum think tank..

 

[astronboy]

I agree that stuffer tubes are not needed as much these days for ejection as the ej charges carry a lot more POW than 'when I was a kid'.

I like them though, even if using only as a laundry basket to assure the correct balance on my scale models that are often 'iffy' in the stability area.... even with simming, the chute must stay up front...

 

[powderburner]

One more advantage of using a stuffer tube---

The internal stuffer tube will contain the ejection gas and prevent it from eating up the inside of your body tube right in front of the motor mount. You may have to replace the stuffer tube (or slip in a new liner) every 20? (30?) flights, but the body tube will remain pristine.

 

[jflis]

"laundry"...

first time I *ever* heard that term used in this context...

...i like it...

 

[Chr$]

Jim,

I'm surprised you've never heard "Laundry" before. Ever since I heard that I have envisioned a flight with perhaps some tighty-whitey's and maybe a bra attached to the shock cord. Heck, maybe use the Bra AS the shock cord.

Hmm... I'm currently building one of your Acme Spitfire's right now. Maybe I'll leave the top section open for something like that...

 

[Fore Check]

Originally posted by jflis
"laundry"...

first time I *ever* heard that term used in this context...

...i like it...

Me too...

"Laundry" is a widely used term in kiting lingo to describe tubes and other "stuff" that you can attach to your flying line for more visual impact. With that in mind, it seems to fit in this application....

 

[jflis]

Originally posted by Chr$
Jim,

I'm surprised you've never heard "Laundry" before. Ever since I heard that I have envisioned a flight with perhaps some tighty-whitey's and maybe a bra attached to the shock cord. Heck, maybe use the Bra AS the shock cord.

Hmm... I'm currently building one of your Acme Spitfire's right now. Maybe I'll leave the top section open for something like that...

People have commented on how amazed they are with how much I know about this or that...

...*i'm* amazed with how much i've yet to learn

Don't waste a good bra as a shock cord... ...you've got a good dual-chute there! LOL

 

[Silverleaf]

*wonders to self...either Jim's wife doesn't read his posts, or hes actually done the dual parachute/bra recovery. In any case, perhaps he's got one in store for a new kit. 8)

 

[Justin]

Astron boy-
Your post on "laundry" made an impact.

Any of you guys know where to fly in the Ft. Lauderdale area..(Florida for you non swamp native Rocketeers....).

 

[xxxREKxxx]

Originally posted by Silverleaf
*wonders to self...either Jim's wife doesn't read his posts, or hes actually done the dual parachute/bra recovery. In any case, perhaps he's got one in store for a new kit. 8)

Sounds like the old joke:

Q. How long have you been using a bra for a parachute?

A. Ever since my wife found it in the back seat of the car!
Bob

 

[prowlerguy]

Gives a whole new meaning to "stuffing your bra", doesn't it?

 

[Chr$]

Originally posted by REK
Sounds like the old joke:

Q. How long have you been using a bra for a parachute?

A. Ever since my wife found it in the back seat of the car!
Bob

ROTFLMAO!!!!!!

 

[Micromeister]

Every time I've mentioned wanting to use a Bra and or pair of "bloomers" as a recovery device for a Barbie Rocket or some such, My Better 2/3rds Wacks me alone side the head " It's a Family Hobby John! Keep it clean" So I moan softly and retreat to the dungon (workshop) in shame

Hummm... maybe I could get away with a Laundry line of things as a streamer;

 

[rstaff3]

So, ma'am, how do you know you husband is having an affair?

(Boohoo) his recovery device was another woman's (boohoo)